The Amtrak conductor wounded in a shooting in Naperville, Illinois, on Tuesday was still in critical condition authorities said Thursday afternoon.

The conductor of the Southwest Chief was identified as Michael Case, 45, of Homewood, Illinois. He was being treated at Edward Hospital in Naperville.

Authorities have taken a suspect into custody but have yet to identify him other than being a man in his 70s from Wisconsin.

Case underwent surgery on Wednesday morning to treat wounds that he suffered in his torso. The shooting occurred after he stepped down to the platform during a scheduled station stop for Amtrak train No. 4.

Police said that Case and a passenger had gotten into an argument before the shooting occurred.

Reports indicate that the suspect shot the conductor from aboard the train. Other passengers restrained the suspect until police arrived.

Naperville police Cmdr. Lou Cammiso said officers have interviewed witnesses and reviewed surveillance footage at the station. Charges are expected to be filed by the DuPage County prosecutor’s office.

“The suspect was on the train; the victim was off the train,” Cammiso said. “Not knowing the intention of the suspect, not knowing what further acts he was capable of, I think it was key that the other passengers did restrain him for police. I think that possibly could have saved lives.”

According to police, the suspect fired one shot during the incident.

A passenger, Mike Leming, of Lake Forest, California, was en route to Chicago where he planned to connect with an Amtrak train to Boston.

He said the argument that preceded the shooting had to do with luggage.

Amtrak officials said over the station’s public address system that police needed to interview passengers who possibly saw something before they could leave.

The announcement said the priority was to get buses for passengers seeking a connecting ride to Cleveland, then “sleepers,” and then everyone else. No. 4 was running two late at the time of the Naperville stop.

“With the assistance of the assistant conductor and several passengers, a suspect was taken into custody by the Naperville Police Department without further incident,” said Amtrak spokesman Marc Magliari. “This senseless and random act of violence is under investigation, and [Amtrak police are] working closely with local law enforcement personnel.”

The Southwest Chief had 239 passengers aboard when it arrived in Naperville and the train was delayed another three hours while police investigated the shooting.

Magliari said Amtrak held connecting passengers at Union Station until passengers from No. 4 could arrive.

He would not speculate about whether Amtrak will change its security procedures.

The passenger carrier prohibits firearms in carry-on baggage along with such other items as archery or martial-arts equipment, corrosive chemicals, hoverboards, flammable liquids or gases and sharp objects such as scissors, nail clippers, corkscrews and razors.